Stacked adhesive optical sensor

ABSTRACT

An optical sensor having a cover layer, an emitter disposed on a first side of the cover, a detector disposed on the first side of said cover, and a plurality of stacked independent adhesive layers disposed on the same first side of the cover, wherein the top most exposed adhesive layer is attached to a patient&#39;s skin. Thus, when the sensor is removed to perform a site check of the tissue location, one of the adhesive layers may also be removed and discarded, exposing a fresh adhesive surface below for re-attachment to a patient&#39;s skin. The independent pieces of the adhesive layers can be serially used to extend the useful life of the product.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/482,258 filed on Jul. 7, 2006, which is a continuation of U.S. patentapplication Ser. No. 10/831,706 filed on Apr. 23, 2004, now U.S. Pat.No. 7,113,815, issued on Sep. 26, 2006, which is a continuation of U.S.patent application Ser. No. 10/256,245, filed on Sep. 25, 2002, now U.S.Pat. No. 6,748,254, issued on Jun. 8, 2004, which is a non-provisionalapplication of U.S. Provisional Application No. 60/328,924 filed on Oct.12, 2001, the full disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to optical sensors, and in particular topulse oximeter sensors.

Many types of optical sensors are used to measure physiologicalcharacteristics of a patient. Typically, an optical sensor providesemitted light which is then scattered through a portion of a patient'stissue and detected. Various characteristics of a patient can bedetermined from analyzing such light, such as oxygen saturation, pulserate, tissue bilirubin, etc.

Pulse oximetry is typically used to measure various blood flowcharacteristics including, but not limited to, the blood-oxygensaturation of hemoglobin in arterial blood, the volume of individualblood pulsations supplying the tissue, and the rate of blood pulsationscorresponding to each heartbeat of a patient. Measurement of thesecharacteristics has been accomplished by use of a non-invasive sensorwhich scatters light through a portion of the patient's tissue whereblood perfuses the tissue, and photoelectrically senses the absorptionof light in such tissue. The amount of light absorbed is then used tocalculate the amount of blood constituent being measured.

The light scattered through the tissue is selected to be of one or morewavelengths that are absorbed by the blood in an amount representativeof the amount of the blood constituent present in the blood. The amountof transmitted light scattered through the tissue will vary inaccordance with the changing amount of blood constituent in the tissueand the related light absorption. For measuring blood oxygen level, suchsensors have typically been provided with a light source that is adaptedto generate light of at least two different wavelengths, and withphotodetectors sensitive to both of those wavelengths, in accordancewith known techniques for measuring blood oxygen saturation.

Known non-invasive sensors include devices that are secured to a portionof the body, such as a finger, an ear or the scalp. In animals andhumans, the tissue of these body portions is perfused with blood and thetissue surface is readily accessible to the sensor.

Certain types of optical sensors are applied to a patient's externaltissue by way of an adhesive attachment, enabled by an adhesive layer onthe sensor. During the monitoring of a patient, there is a need toremove the sensor to perform a site check of the tissue location, andthis removal typically damages the adhesive layer. Furthermore, adhesivetype sensors are often used with disposable type sensors where the photoemitter and the detector are mounted on a backing without the benefit ofa rigid optical mount to maintain the emitter and detector's separationrelatively fixed, and thus the sensor is subject to motion inducedartifacts that may adversely affect measurement accuracy.

There is therefore a need to improve the functionality of adhesive-typeoptical sensors.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an optical sensor having a cover layer,an emitter disposed on a first side of the cover, a detector disposed onthe first side of said cover, and a plurality of stacked independentadhesive layers disposed on the same first side of the cover, whereinthe top most exposed adhesive layer is attached to a patient's skin.Thus, when the sensor is removed to perform a site check of the tissuelocation, one of the adhesive layers may also be removed and discarded,exposing a fresh adhesive surface below for re-attachment to a patient'sskin. The independent pieces of the adhesive layers can be serially usedto extend the useful life of the product.

One aspect of the present invention is directed towards using agenerally annulus-shaped adhesive layer that surround the emitter andthe detector and thus avoids having any adhesive present between theemitter and the detector to minimize optical shunt, which is known toadversely affect measurement accuracy.

Another aspect of the present invention is directed towards usingoptical lenses made from a soft or compliant material such as anoptically transparent PVC material to minimize tissue necrosis.

Another aspect of the invention is directed towards the use of asemi-rigid optical mount structure to hold the emitter and the detectorin place to maintain the separation between the electro-optics (emitterand detector) relatively fixed and yet allow a certain minimal amount oftorque and twisting to occur as the sensor is applied. The semi-rigidoptical mount, by maintaining the separation relatively fixed reducesmotion induced artifacts in the detected electro-optic signals, whichmay adversely interfere with measurement accuracy. For a furtherunderstanding of the nature and advantages of the present invention,reference should be made to the following description in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective disassembled view of the sensor according to anembodiment of the present invention.

FIG. 2 is a perspective view of the sensor according to an embodiment ofthe present invention.

FIG. 3 is a top view of the embodiment of FIG. 2.

FIG. 4 is a sectional view “A-A” of FIG. 3.

FIG. 5 is a perspective view of an alternate embodiment of the sensor ofthe present invention having a hinged lid.

FIG. 6 is a diagram showing the sensor of FIG. 5 positioned on a patientduring a site check.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a perspective disassembled view of the sensor 100 according toan embodiment of the present invention. The sensor includes a sensor top1 or cover layer which is exposed to the ambient environment when thesensor is attached to a patient's skin. In one embodiment, the coverlayer 1 is fabricated of a common PVC foam. Alternately, the cover layer1 is fabricated of a urethane foam material and particularly, an opencell breathable urethane foam such as, for example, the PORON™ family ofurethanes commercially available from the Rogers corporation ofConnecticut. A mask layer 2 preferably including a metalized plasticfilm is adhesively attached to the cover layer 1. In a preferredembodiment, the metalized masked layer 2 is an aluminized polypropylenefilm with a synthetic adhesive layer for attachment to the cover layer1. The metalized mask layer 2 is so placed to prevent, minimize orreject secondary light from interfering with the photodetector 7. Asused herein, secondary light includes all light that originates fromsources other than the emitter 11, and which may have originated fromsources including ambient or surgical light sources. An emitter 11 isplaced above the mask layer 2. The emitter 11 is configured to directlight at predetermined wavelengths at a patient's skin. The lightdirected to the patient's skin is scattered through the patient's tissueand is selected to be of one or more wavelengths that are absorbed bythe blood in an amount representative of the amount of blood constituentpresent in the body. A photo detector 7 is also placed above the masklayer 2 and adjacent to the emitter 11 to detect the amount of lightthat has been diffused through the patient's tissue. The amount of lightthat has diffused through the patient's tissue will vary in accordancewith the changing amount of blood constituent in the tissue and therelated light absorption.

For measuring blood oxygen level, the emitter is adapted to generatelight of at least two different wavelengths, in accordance with knowntechniques for measuring blood oxygen saturation. The sensor, whenadapted for blood oxygen saturation is useable for not only adultpatients, but may also be adapted for use for neonatal and pediatricpatients. Adaptations for neonatal and pediatric use may includeaccommodations of size and/or adhesive materials more compatible withthe geometry and skin characteristics of those patients. Further, thesensor may optionally use emitters of different wavelengths and hencemay use emitter and detector combinations that lead to more accuratereadings at low blood oxygen saturations, which is the case for somepatients. Light sources which are optimized for low oxygen saturationranges are described in U.S. Pat. No. 5,782,237, entitled: “PulseOximeter and Sensor Optimized for Low Saturation,” assigned to theassignee herein, the disclosure of which is hereby incorporated byreference herein in its entirety.

A Faraday shield 5 is placed in front of photodetector 7 to reduce theeffect of extrinsic electrical fields that could adversely affect theelectrical signal from the photodetector. A semi-rigid optical mount 6is placed above the mask layer 2, and which surrounds and holds theemitter 11 and the detector 7 in a manner to maintain the separationbetween the emitter 11 and the detector 7 fixed and yet allow a certainminimal amount of flexing and twisting to occur as the sensor is appliedto a patient. Without the semi-rigid optical mount in place, torque canoften cause orientation changes between the emitter 11 and the detector7 which can interfere with the accuracy of the measurements obtained bythe sensor through changes in calibration and motion-induced artifact.Furthermore, the semi-rigid optical mount 6 substantially reduces theflex and the twist which may also create significant motion artifact,which is also known to adversely affect measurement accuracy. In oneembodiment, the semi-rigid optical mount 6 is manufactured from a blackpolypropylene material. The black color of the optical mount alsoreduces the potential for optical shunt between the emitter and thedetector, which can also cause measurement inaccuracies. Windows orlenses 4 are attached or bonded using a suitable adhesive (e.g., anultraviolet cure adhesive process), one each to the detector and theemitter to assist in coupling the light emitted from the emitter 11 intothe tissue, and collected from the tissue and directed towards thedetector 7. In one embodiment, the lenses 4 are made of an opticallytransparent plastic material to minimize optical attenuation. In analternate embodiment, the lenses 4 are made of a compliant material suchas a transparent PVC, urethanes, or room temperature vulcanized (RTV)material, and so on. The choice of selecting a compliant material forthe lenses is driven by the desire to prevent the possibility ofnecrosis of the skin, when the sensor is applied to the patient.Preferably, the compliant material has a hardness of less than 60 on aShore A durometer scale. Alternately, or in addition to the lenses, theemitter and/or the detector arrangements may also include opticaldiffusers. The advantage of using optical diffusers is that the sensorwould have less sensitivity to tissue heterogeneity, and thus providemore uniform and more accurate results.

A mask layer 3 is adhesively connected with the parts below it. The masklayer 3 has openings therein that fit over and surround the opticalmount 6 placed below it (the mask layer 3). The mask layer 3 serves as asubstantially flat platform for the subsequent attachment of the stackof adhesive layers. In one embodiment, the mask layer is fabricated froma cellular urethane foam such as the PORON™ family of urethane foams,and is attached to the cover layer 1 using a pressure sensitiveadhesive. Lastly, a stack of adhesive layers 8, 9, and 10 are placedabove the mask layer 3. The lower most adhesive layer 9 is attached tothe mask layer 3 using an acrylic transfer adhesive. While in oneembodiment a stack of three adhesive layers is placed above the masklayer 3, other multiple stacked adhesive layers are also within thescope of the embodiments of the present invention.

In one embodiment, the adhesive layers are in a ring shape so that noadhesive is present between the photo emitter 11 and the photo detector7, thereby minimizing optical shunt between the photo emitter and thephoto detector, which is known to lead to measurement inaccuracies. Theadhesive layers or rings may be manufactured of a polyethylene filmhaving an acrylic adhesive on one side for attachment to the patient'stissue. Alternately, the adhesive layers or rings may have an adhesivelayers on both sides, in which case the adhesive layers are separatedfrom one another by release layers (e.g. release paper). Preferably, theadhesive layers include a non-adhesive tab portion (e.g. 8 a), arrangedstacked or in a fanned-out array, to enable the clinician to easily graband remove the used adhesive layer to expose the layer below. The tabportions may be non-adhesive colored tabs (e.g., green, yellow, red,lavender, orange) to enable the easy removal of the adhesive rings.Additionally, another release layer (not shown) is placed above thestack of adhesive layers to cover the very first adhesive layer while itis in storage.

In certain embodiments, the adhesive rings are black to minimizereflected light, which is known to impact the accuracy of optical-basedmeasurements. In certain embodiments, the adhesive rings are thermallystable, so that the adhesion between the rings is not compromised as aresult of exposure to heat. Additionally, the adhesive rings may includea release agent, such as, for example, a low molecular weight siliconeoil on the back side of the ring, in order to minimize or preventadjacent rings from sticking to one another. Various alternate ringconstruction may be employed, including a continuous 0.001 inch thickpolyethylene film with acrylic pressure sensitive adhesive on one side.The continuous film can be made of other materials such as polyester,polyimide or Teflon, to achieve specific strength, release andtemperature stability requirements. The adhesives used on the surface ofthe film can be acrylic, synthetic rubber, natural rubber (e.g., latex)or other non-toxic adhesive. The ring may include a paper with a releaseagent on one side as the carrier film. This allows printing on eachrelease liner, user information such as “adhesive layer #1” or can beinked black to control optical shunt.

Alternately, the adhesive rings need not be in a ring shape, but may becontinuous adhesive surface, with a black strip between the emitter anddetector in order to minimize optical shunt.

The pre-attached stacks of adhesive layers enables the extended use of adisposable adhesive-type sensor. A desired feature for sensors is theability to check the sensor site periodically (e.g. once every 12hours), and remain capable of continuous use for multiple days. In priordisposable sensors which were adhesively attached to a patient's skin,multiple cycles of repositioning the sensor was not possible due to thedegradation of the adhesive and the sloughing nature of the tissuebeneath the sensor attachment location. This failed reattachment wouldnecessitate the replacement of the sensor in its entirety, which wouldincrease the overall cost of the patient monitoring procedure. However,with the use of a stack of pre-attached adhesive rings, when the sensoris removed to perform a site check, one of the adhesive layers may alsobe removed exposing a fresh adhesive surface below. Thus, having severalindependent pieces of adhesive layers that can be serially used, extendsthe useful life of the product and reduces the overall costs of thepatient monitoring procedure.

FIG. 2 is a perspective view of the assembled sensor 100. This figure(FIG. 2) shows the top most adhesive layer 8, and lenses 4 covering thephoto emitter 11 and photo detector 7. Furthermore, FIG. 2 shows cable14 attached to the sensor 100. Tab portions 1 a and 1 b (shown inFIG. 1) wrap around the cable 14 to hold the cable and the sensor in astable manner. Cable 14 attaches to the photo emitter 11 and detector 7via traces or wires (not shown).

FIG. 3 is a top view of the embodiment of FIG. 2. FIG. 3 also shows thetop most adhesive layer 8, and lenses 4 covering the photo emitter 11and photo detector 7. Furthermore, FIG. 2 shows cable 14 attached to thesensor 100. FIG. 4 shows sectional view “A-A” of FIG. 3. FIG. 4 showsthe cover layer 1, the top most adhesive layer 8 and lenses 4 which areplaced above the photo emitter 11 and photo detector 7. As can be seenfrom FIG. 4, the sensor 100 is substantially flat, while the lenses 4protrude outward from a plane of the sensor. Thus, when attached, thelenses push on the patient's tissue location (e.g. forehead) to enhancelight coupling and the depth of optical penetration by pressing mildlyinto the skin. Since the lenses protrude outward from the sensor plane,the adjacent adhesive layers necessarily lie in a plane which is offsetor away from the patient's tissue location, thus “pulling” the lensesinto the skin during use. This assures good optical contact betweensensor and tissue, and reduces the potential, contribution of lightshunting.

FIG. 5 is a perspective view of an alternate embodiment of the sensor200 of the present invention having a hinged lid. The sensor 200includes a ring-shaped layer 202 having an adhesive side, which isconfigured to be attached to a patient during monitoring. The sensor 200also includes a hinged lid 204 which holds the necessary electro-opticsincluding a photo emitter and a photo detector (not shown) as describedabove. The hinged lid 204 is coupled to the ring-shaped adhesive layer202 by a hinged connection 208 that enables the lifting and the checkingof the sensor site without the need to remove the sensor from thepatient. Cable 210 provides the leads or wires connected with the photodetector and photo emitter for the proper operation of the sensor. Aclasp 206 secures the hinged lid 204 in a position effective for patientmonitoring. The clasp 206 is also used by a clinician to lift the hingedlid 204 for checking the sensor site. In one embodiment, the clasp 206adhesively engages the ring-shaped layer 202. In an alternateembodiment, the clasp 206 engages the ring-shaped layer via a mechanicalclasp-type connection. The ring-shaped layer 202 may also incorporate astacked adhesive arrangement as described above to enable the repeatedremoval and re-attachment of the sensor to the patient.

FIG. 6 is a diagram showing the sensor of FIG. 5 positioned on a patientduring a site check. As can be seen from this figure (FIG. 6), thering-shaped layer 202 is adhesively attached to a patient, while thehinged lid 204 containing the photo emitter 212 and photo detector 214is lifted from the patient's forehead to enable the checking of thetissue location underneath the sensor site. Cable 210 provides the leadsor wires connected with the photo detector and photo emitter for theproper operation of the sensor.

The multiple stacked adhesive layer embodiments and the hinged lidembodiments of the present invention may be also be used to improve theoperation of any disposable sensor and particularly disposable oximetersensors. These disposable sensors include sensors based on thereflectance of light from tissue to the detector (as described abovewith the emitter and the detector placed on the same side of the tissue)as well as transmissive type sensors, where the emitter and the detectorare placed on opposite sides of a tissue site being probed. Examples ofsensors that can incorporate the multiple stacked adhesive layerembodiments or the hinged-lid embodiments include the adhesive, andreusable sensors for use at various tissue locations, including thefinger tip, foot, nose, and forehead locations such as the D-20, D-25,N-25, I-20, R-15, as well as the A, N, I, and P series of sensorsmanufactured by the assignee herein.

Furthermore, the multiple stacked adhesive layer embodiments and thehinged lid embodiments of the present invention are not only useable foradult patients, but are also useable with patients on whom it issometimes preferable to use a soft gel adhesive to minimize theoccurrence of tearing of the skin. Such patients include geriatric,pediatric or neonatal patients. The inclusion of a soft gel in anoptical sensor is described in U.S. Pat. No. 5,830,136, entitled: “GelPad Optical Sensor,” assigned to the assignee herein, the disclosure ofwhich is hereby incorporated herein in its entirety. An alternateembodiment of a soft gel adhesive includes only a single adhesive layer(not stacked), since some gel materials can be cleaned with water orother liquid agents to refresh the adhesive properties. As such, the useof multiple layers of gel adhesive may not be required for limited butmultiple sensor placements on an individual patient.

As will be understood by those skilled in the art, the present inventionmay be embodied in other specific forms without departing from theessential characteristics thereof. For example, the disposable sensormay be a forehead or a nasal sensor, the sensor may be configured foruse on an adult, pediatric or neonatal patient, the sensor may useseveral possible arrangements of adhesive layers arranged in an stackedmanner, or the sensor may use suitable materials other than thosedescribed above. These other embodiments are intended to be includedwithin the scope of the present invention, which is set forth in thefollowing claims.

The invention claimed is:
 1. A method of applying a sensor, comprising:providing a flexible sensor body to which an emitter and a detector arecoupled, wherein the flexible sensor body is coupled to a plurality ofstacked adhesive layers, wherein no portion of the plurality of stackedadhesive layers is in the direct optical path between the emitter andthe detector, and wherein each adhesive layer of the plurality ofstacked adhesive layers comprises a ring shape that surrounds both theemitter and the detector such that there is no adhesive present in thedirect optical path between the emitter and the detector; removing thefirst adhesive layer from the plurality of stacked adhesive layers,wherein removing the first adhesive layer exposes a second adhesivelayer within the plurality of stacked adhesive layers; and applying thesecond adhesive layer to a patient, wherein the second adhesive layer isconfigured to secure the flexible sensor body to the patient's skin. 2.The method of claim 1, wherein the sensor is a pulse oximetry sensor. 3.The method of claim 1, comprising: removing the sensor from thepatient's tissue; removing the second adhesive layer to expose a thirdadhesive layer; and applying the third adhesive layer to the patient'stissue.
 4. The method of claim 1, comprising: removing a release layerfrom the first adhesive layer; and applying the first adhesive layer tothe patient's tissue.
 5. The method of claim 1, comprising: removing arelease layer from the second adhesive layer before applying the secondadhesive layer to the patient's tissue.
 6. The method of claim 1,comprising removing each of the plurality of adhesive layers on aperiodic schedule.
 7. The method of claim 6, comprising disposing of thesensor after a final adhesive layer is applied to the patient's tissue.8. The method of claim 1, wherein the plurality of stacked adhesivelayers are independent nonmetallic layers.
 9. The method of claim 1,wherein at least one of the plurality of adhesive layers is black and isconfigured to reduce optical shunting between the emitter and thedetector.
 10. The method of claim 1, wherein the first and secondadhesive layers are separated by a release agent configured to minimizethe first and second adhesive layers from sticking to one another. 11.The method of claim 1, wherein the second adhesive layer has a firstside and a second side, and wherein the first side has an acrylicadhesive configured to attach to the patient's skin.
 12. The method ofclaim 11, wherein the second side has an acrylic adhesive configured toattach to a third adhesive layer.
 13. A method of manufacturing a pulseoximetry sensor, comprising: providing a flexible sensor body to whichan emitter and a detector are coupled; providing a plurality of adhesivelayers coupled to the sensor body, wherein no portion of the pluralityof adhesive layers is in the direct optical path between the emitter andthe detector, and wherein each adhesive layer of the plurality ofstacked adhesive layers comprises a ring shape that surrounds both theemitter and the detector such that there is no adhesive present in thedirect optical path between the emitter and the detector; and providingeach of the plurality of adhesive layers with respective non-adhesivetabs, wherein a first non-adhesive tab is configured to separate a firstadhesive layer from the plurality of adhesive layers to expose a secondadhesive layer within the plurality of adhesive layers.
 14. The methodof claim 13, comprising providing a release layer on the first adhesivelayer.
 15. The method of claim 13, comprising providing release layersbetween the plurality of nonadhesive layers.
 16. The method of claim 15,comprising providing indicators on each respective release layerindicating a position within the plurality of adhesive layers.
 17. Themethod of claim 13, wherein each of the respective non-adhesive tabs isa different color.
 18. The method of claim 13, wherein the respectivenon-adhesive tabs are arranged in a fan configuration.
 19. The method ofclaim 13, comprising providing a mask layer disposed between theflexible sensor body and the plurality of adhesive layers.